The present invention relates to a two-component start developer containing a toner and a carrier at a predetermined ratio, to be used for an image forming apparatus such as an electrostatic copying apparatus, a laser beam printer or the like.
In the image forming apparatus, the surface of a photoreceptor is exposed to light to form an electrostatic latent image on the surface of the photoreceptor. By a developing device, a developer is allowed to come in contact with the surface of the photoreceptor. The toner contained in the developer is electrostatically stuck the electrostatic latent image, so that the electrostatic latent image is formed into a toner image. From the photoreceptor surface, the toner image is transferred to and fixed on paper. Thus, an image corresponding to the electrostatic latent image is formed on the paper surface.
As the developer, there is generally used a two-component developer containing a toner and a carrier which is adapted to circulate in the developing device while adsorbing the toner. The developer which is first used in the developing device, is called a start developer containing a toner and a carrier at a predetermined ratio.
The characteristics of the start developer include, in addition to the blending ratio of the toner and the carrier, the amount of electric charge based on the image density at the initial image forming stage, the occurrence or non-occurrence of toner scattering and the like.
In spite of the determination of the characteristics above-mentioned, the start developer presents, over a period from the initial image forming stage to the stable image forming stage after repetition of about 3000 image formings, a variety of problems of unstable toner density, subsequent insufficient image density and image deterioration such as fog, toner scattering, decrease in resolution or the like.